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                                <h1 id="&#x6570;&#x636E;&#x7C7B;&#x578B;&#x7684;&#x8F6C;&#x6362;">&#x6570;&#x636E;&#x7C7B;&#x578B;&#x7684;&#x8F6C;&#x6362;</h1>
<h2 id="&#x6982;&#x8FF0;">&#x6982;&#x8FF0;</h2>
<p>JavaScript &#x662F;&#x4E00;&#x79CD;&#x52A8;&#x6001;&#x7C7B;&#x578B;&#x8BED;&#x8A00;&#xFF0C;&#x53D8;&#x91CF;&#x6CA1;&#x6709;&#x7C7B;&#x578B;&#x9650;&#x5236;&#xFF0C;&#x53EF;&#x4EE5;&#x968F;&#x65F6;&#x8D4B;&#x4E88;&#x4EFB;&#x610F;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> x = y ? <span class="hljs-number">1</span> : <span class="hljs-string">&apos;a&apos;</span>;
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x53D8;&#x91CF;<code>x</code>&#x5230;&#x5E95;&#x662F;&#x6570;&#x503C;&#x8FD8;&#x662F;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x53D6;&#x51B3;&#x4E8E;&#x53E6;&#x4E00;&#x4E2A;&#x53D8;&#x91CF;<code>y</code>&#x7684;&#x503C;&#x3002;<code>y</code>&#x4E3A;<code>true</code>&#x65F6;&#xFF0C;<code>x</code>&#x662F;&#x4E00;&#x4E2A;&#x6570;&#x503C;&#xFF1B;<code>y</code>&#x4E3A;<code>false</code>&#x65F6;&#xFF0C;<code>x</code>&#x662F;&#x4E00;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x3002;&#x8FD9;&#x610F;&#x5473;&#x7740;&#xFF0C;<code>x</code>&#x7684;&#x7C7B;&#x578B;&#x6CA1;&#x6CD5;&#x5728;&#x7F16;&#x8BD1;&#x9636;&#x6BB5;&#x5C31;&#x77E5;&#x9053;&#xFF0C;&#x5FC5;&#x987B;&#x7B49;&#x5230;&#x8FD0;&#x884C;&#x65F6;&#x624D;&#x80FD;&#x77E5;&#x9053;&#x3002;</p>
<p>&#x867D;&#x7136;&#x53D8;&#x91CF;&#x7684;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x662F;&#x4E0D;&#x786E;&#x5B9A;&#x7684;&#xFF0C;&#x4F46;&#x662F;&#x5404;&#x79CD;&#x8FD0;&#x7B97;&#x7B26;&#x5BF9;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x662F;&#x6709;&#x8981;&#x6C42;&#x7684;&#x3002;&#x5982;&#x679C;&#x8FD0;&#x7B97;&#x7B26;&#x53D1;&#x73B0;&#xFF0C;&#x8FD0;&#x7B97;&#x5B50;&#x7684;&#x7C7B;&#x578B;&#x4E0E;&#x9884;&#x671F;&#x4E0D;&#x7B26;&#xFF0C;&#x5C31;&#x4F1A;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x7C7B;&#x578B;&#x3002;&#x6BD4;&#x5982;&#xFF0C;&#x51CF;&#x6CD5;&#x8FD0;&#x7B97;&#x7B26;&#x9884;&#x671F;&#x5DE6;&#x53F3;&#x4E24;&#x4FA7;&#x7684;&#x8FD0;&#x7B97;&#x5B50;&#x5E94;&#x8BE5;&#x662F;&#x6570;&#x503C;&#xFF0C;&#x5982;&#x679C;&#x4E0D;&#x662F;&#xFF0C;&#x5C31;&#x4F1A;&#x81EA;&#x52A8;&#x5C06;&#x5B83;&#x4EEC;&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-string">&apos;4&apos;</span> - <span class="hljs-string">&apos;3&apos;</span> <span class="hljs-comment">// 1</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x867D;&#x7136;&#x662F;&#x4E24;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x76F8;&#x51CF;&#xFF0C;&#x4F46;&#x662F;&#x4F9D;&#x7136;&#x4F1A;&#x5F97;&#x5230;&#x7ED3;&#x679C;&#x6570;&#x503C;<code>1</code>&#xFF0C;&#x539F;&#x56E0;&#x5C31;&#x5728;&#x4E8E; JavaScript &#x5C06;&#x8FD0;&#x7B97;&#x5B50;&#x81EA;&#x52A8;&#x8F6C;&#x4E3A;&#x4E86;&#x6570;&#x503C;&#x3002;</p>
<p>&#x672C;&#x7AE0;&#x8BB2;&#x89E3;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x7684;&#x89C4;&#x5219;&#x3002;&#x5728;&#x6B64;&#x4E4B;&#x524D;&#xFF0C;&#x5148;&#x8BB2;&#x89E3;&#x5982;&#x4F55;&#x624B;&#x52A8;&#x5F3A;&#x5236;&#x8F6C;&#x6362;&#x6570;&#x636E;&#x7C7B;&#x578B;&#x3002;</p>
<h2 id="&#x5F3A;&#x5236;&#x8F6C;&#x6362;">&#x5F3A;&#x5236;&#x8F6C;&#x6362;</h2>
<p>&#x5F3A;&#x5236;&#x8F6C;&#x6362;&#x4E3B;&#x8981;&#x6307;&#x4F7F;&#x7528;<code>Number()</code>&#x3001;<code>String()</code>&#x548C;<code>Boolean()</code>&#x4E09;&#x4E2A;&#x51FD;&#x6570;&#xFF0C;&#x624B;&#x52A8;&#x5C06;&#x5404;&#x79CD;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5206;&#x522B;&#x8F6C;&#x6362;&#x6210;&#x6570;&#x5B57;&#x3001;&#x5B57;&#x7B26;&#x4E32;&#x6216;&#x8005;&#x5E03;&#x5C14;&#x503C;&#x3002;</p>
<h3 id="number">Number()</h3>
<p>&#x4F7F;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#xFF0C;&#x53EF;&#x4EE5;&#x5C06;&#x4EFB;&#x610F;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x8F6C;&#x5316;&#x6210;&#x6570;&#x503C;&#x3002;</p>
<p>&#x4E0B;&#x9762;&#x5206;&#x6210;&#x4E24;&#x79CD;&#x60C5;&#x51B5;&#x8BA8;&#x8BBA;&#xFF0C;&#x4E00;&#x79CD;&#x662F;&#x53C2;&#x6570;&#x662F;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x53E6;&#x4E00;&#x79CD;&#x662F;&#x53C2;&#x6570;&#x662F;&#x5BF9;&#x8C61;&#x3002;</p>
<p><strong>&#xFF08;1&#xFF09;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x503C;</strong></p>
<p>&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x503C;&#x7684;&#x8F6C;&#x6362;&#x89C4;&#x5219;&#x5982;&#x4E0B;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-comment">// &#x6570;&#x503C;&#xFF1A;&#x8F6C;&#x6362;&#x540E;&#x8FD8;&#x662F;&#x539F;&#x6765;&#x7684;&#x503C;</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-number">324</span>) <span class="hljs-comment">// 324</span>

<span class="hljs-comment">// &#x5B57;&#x7B26;&#x4E32;&#xFF1A;&#x5982;&#x679C;&#x53EF;&#x4EE5;&#x88AB;&#x89E3;&#x6790;&#x4E3A;&#x6570;&#x503C;&#xFF0C;&#x5219;&#x8F6C;&#x6362;&#x4E3A;&#x76F8;&#x5E94;&#x7684;&#x6570;&#x503C;</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-string">&apos;324&apos;</span>) <span class="hljs-comment">// 324</span>

<span class="hljs-comment">// &#x5B57;&#x7B26;&#x4E32;&#xFF1A;&#x5982;&#x679C;&#x4E0D;&#x53EF;&#x4EE5;&#x88AB;&#x89E3;&#x6790;&#x4E3A;&#x6570;&#x503C;&#xFF0C;&#x8FD4;&#x56DE; NaN</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-string">&apos;324abc&apos;</span>) <span class="hljs-comment">// NaN</span>

<span class="hljs-comment">// &#x7A7A;&#x5B57;&#x7B26;&#x4E32;&#x8F6C;&#x4E3A;0</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-string">&apos;&apos;</span>) <span class="hljs-comment">// 0</span>

<span class="hljs-comment">// &#x5E03;&#x5C14;&#x503C;&#xFF1A;true &#x8F6C;&#x6210; 1&#xFF0C;false &#x8F6C;&#x6210; 0</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-literal">true</span>) <span class="hljs-comment">// 1</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-literal">false</span>) <span class="hljs-comment">// 0</span>

<span class="hljs-comment">// undefined&#xFF1A;&#x8F6C;&#x6210; NaN</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-literal">undefined</span>) <span class="hljs-comment">// NaN</span>

<span class="hljs-comment">// null&#xFF1A;&#x8F6C;&#x6210;0</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-literal">null</span>) <span class="hljs-comment">// 0</span>
</code></pre>
<p><code>Number</code>&#x51FD;&#x6570;&#x5C06;&#x5B57;&#x7B26;&#x4E32;&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#xFF0C;&#x8981;&#x6BD4;<code>parseInt</code>&#x51FD;&#x6570;&#x4E25;&#x683C;&#x5F88;&#x591A;&#x3002;&#x57FA;&#x672C;&#x4E0A;&#xFF0C;&#x53EA;&#x8981;&#x6709;&#x4E00;&#x4E2A;&#x5B57;&#x7B26;&#x65E0;&#x6CD5;&#x8F6C;&#x6210;&#x6570;&#x503C;&#xFF0C;&#x6574;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x5C31;&#x4F1A;&#x88AB;&#x8F6C;&#x4E3A;<code>NaN</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">parseInt</span>(<span class="hljs-string">&apos;42 cats&apos;</span>) <span class="hljs-comment">// 42</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-string">&apos;42 cats&apos;</span>) <span class="hljs-comment">// NaN</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;<code>parseInt</code>&#x9010;&#x4E2A;&#x89E3;&#x6790;&#x5B57;&#x7B26;&#xFF0C;&#x800C;<code>Number</code>&#x51FD;&#x6570;&#x6574;&#x4F53;&#x8F6C;&#x6362;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x7C7B;&#x578B;&#x3002;</p>
<p>&#x53E6;&#x5916;&#xFF0C;<code>parseInt</code>&#x548C;<code>Number</code>&#x51FD;&#x6570;&#x90FD;&#x4F1A;&#x81EA;&#x52A8;&#x8FC7;&#x6EE4;&#x4E00;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x524D;&#x5BFC;&#x548C;&#x540E;&#x7F00;&#x7684;&#x7A7A;&#x683C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">parseInt</span>(<span class="hljs-string">&apos;\t\v\r12.34\n&apos;</span>) <span class="hljs-comment">// 12</span>
<span class="hljs-built_in">Number</span>(<span class="hljs-string">&apos;\t\v\r12.34\n&apos;</span>) <span class="hljs-comment">// 12.34</span>
</code></pre>
<p><strong>&#xFF08;2&#xFF09;&#x5BF9;&#x8C61;</strong></p>
<p>&#x7B80;&#x5355;&#x7684;&#x89C4;&#x5219;&#x662F;&#xFF0C;<code>Number</code>&#x65B9;&#x6CD5;&#x7684;&#x53C2;&#x6570;&#x662F;&#x5BF9;&#x8C61;&#x65F6;&#xFF0C;&#x5C06;&#x8FD4;&#x56DE;<code>NaN</code>&#xFF0C;&#x9664;&#x975E;&#x662F;&#x5305;&#x542B;&#x5355;&#x4E2A;&#x6570;&#x503C;&#x7684;&#x6570;&#x7EC4;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">Number</span>({a: <span class="hljs-number">1</span>}) <span class="hljs-comment">// NaN</span>
<span class="hljs-built_in">Number</span>([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]) <span class="hljs-comment">// NaN</span>
<span class="hljs-built_in">Number</span>([<span class="hljs-number">5</span>]) <span class="hljs-comment">// 5</span>
</code></pre>
<p>&#x4E4B;&#x6240;&#x4EE5;&#x4F1A;&#x8FD9;&#x6837;&#xFF0C;&#x662F;&#x56E0;&#x4E3A;<code>Number</code>&#x80CC;&#x540E;&#x7684;&#x8F6C;&#x6362;&#x89C4;&#x5219;&#x6BD4;&#x8F83;&#x590D;&#x6742;&#x3002;</p>
<p>&#x7B2C;&#x4E00;&#x6B65;&#xFF0C;&#x8C03;&#x7528;&#x5BF9;&#x8C61;&#x81EA;&#x8EAB;&#x7684;<code>valueOf</code>&#x65B9;&#x6CD5;&#x3002;&#x5982;&#x679C;&#x8FD4;&#x56DE;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5219;&#x76F4;&#x63A5;&#x5BF9;&#x8BE5;&#x503C;&#x4F7F;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#xFF0C;&#x4E0D;&#x518D;&#x8FDB;&#x884C;&#x540E;&#x7EED;&#x6B65;&#x9AA4;&#x3002;</p>
<p>&#x7B2C;&#x4E8C;&#x6B65;&#xFF0C;&#x5982;&#x679C;<code>valueOf</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x8FD8;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x5219;&#x6539;&#x4E3A;&#x8C03;&#x7528;&#x5BF9;&#x8C61;&#x81EA;&#x8EAB;&#x7684;<code>toString</code>&#x65B9;&#x6CD5;&#x3002;&#x5982;&#x679C;<code>toString</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5219;&#x5BF9;&#x8BE5;&#x503C;&#x4F7F;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#xFF0C;&#x4E0D;&#x518D;&#x8FDB;&#x884C;&#x540E;&#x7EED;&#x6B65;&#x9AA4;&#x3002;</p>
<p>&#x7B2C;&#x4E09;&#x6B65;&#xFF0C;&#x5982;&#x679C;<code>toString</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x5C31;&#x62A5;&#x9519;&#x3002;</p>
<p>&#x8BF7;&#x770B;&#x4E0B;&#x9762;&#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> obj = {x: <span class="hljs-number">1</span>};
<span class="hljs-built_in">Number</span>(obj) <span class="hljs-comment">// NaN</span>

<span class="hljs-comment">// &#x7B49;&#x540C;&#x4E8E;</span>
<span class="hljs-keyword">if</span> (<span class="hljs-keyword">typeof</span> obj.valueOf() === <span class="hljs-string">&apos;object&apos;</span>) {
  <span class="hljs-built_in">Number</span>(obj.toString());
} <span class="hljs-keyword">else</span> {
  <span class="hljs-built_in">Number</span>(obj.valueOf());
}
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;<code>Number</code>&#x51FD;&#x6570;&#x5C06;<code>obj</code>&#x5BF9;&#x8C61;&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#x3002;&#x80CC;&#x540E;&#x53D1;&#x751F;&#x4E86;&#x4E00;&#x8FDE;&#x4E32;&#x7684;&#x64CD;&#x4F5C;&#xFF0C;&#x9996;&#x5148;&#x8C03;&#x7528;<code>obj.valueOf</code>&#x65B9;&#x6CD5;, &#x7ED3;&#x679C;&#x8FD4;&#x56DE;&#x5BF9;&#x8C61;&#x672C;&#x8EAB;&#xFF1B;&#x4E8E;&#x662F;&#xFF0C;&#x7EE7;&#x7EED;&#x8C03;&#x7528;<code>obj.toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x8FD9;&#x65F6;&#x8FD4;&#x56DE;&#x5B57;&#x7B26;&#x4E32;<code>[object Object]</code>&#xFF0C;&#x5BF9;&#x8FD9;&#x4E2A;&#x5B57;&#x7B26;&#x4E32;&#x4F7F;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#xFF0C;&#x5F97;&#x5230;<code>NaN</code>&#x3002;</p>
<p>&#x9ED8;&#x8BA4;&#x60C5;&#x51B5;&#x4E0B;&#xFF0C;&#x5BF9;&#x8C61;&#x7684;<code>valueOf</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x5BF9;&#x8C61;&#x672C;&#x8EAB;&#xFF0C;&#x6240;&#x4EE5;&#x4E00;&#x822C;&#x603B;&#x662F;&#x4F1A;&#x8C03;&#x7528;<code>toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x800C;<code>toString</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x5BF9;&#x8C61;&#x7684;&#x7C7B;&#x578B;&#x5B57;&#x7B26;&#x4E32;&#xFF08;&#x6BD4;&#x5982;<code>[object Object]</code>&#xFF09;&#x3002;&#x6240;&#x4EE5;&#xFF0C;&#x4F1A;&#x6709;&#x4E0B;&#x9762;&#x7684;&#x7ED3;&#x679C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">Number</span>({}) <span class="hljs-comment">// NaN</span>
</code></pre>
<p>&#x5982;&#x679C;<code>toString</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x4E0D;&#x662F;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x7ED3;&#x679C;&#x5C31;&#x4F1A;&#x62A5;&#x9519;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> obj = {
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> {};
  },
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> {};
  }
};

<span class="hljs-built_in">Number</span>(obj)
<span class="hljs-comment">// TypeError: Cannot convert object to primitive value</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x7684;<code>valueOf</code>&#x548C;<code>toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x8FD4;&#x56DE;&#x7684;&#x90FD;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x6240;&#x4EE5;&#x8F6C;&#x6210;&#x6570;&#x503C;&#x65F6;&#x4F1A;&#x62A5;&#x9519;&#x3002;</p>
<p>&#x4ECE;&#x4E0A;&#x4F8B;&#x8FD8;&#x53EF;&#x4EE5;&#x770B;&#x5230;&#xFF0C;<code>valueOf</code>&#x548C;<code>toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x90FD;&#x662F;&#x53EF;&#x4EE5;&#x81EA;&#x5B9A;&#x4E49;&#x7684;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">Number</span>({
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">2</span>;
  }
})
<span class="hljs-comment">// 2</span>

<span class="hljs-built_in">Number</span>({
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">3</span>;
  }
})
<span class="hljs-comment">// 3</span>

<span class="hljs-built_in">Number</span>({
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">2</span>;
  },
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">3</span>;
  }
})
<span class="hljs-comment">// 2</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5BF9;&#x4E09;&#x4E2A;&#x5BF9;&#x8C61;&#x4F7F;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#x3002;&#x7B2C;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x8FD4;&#x56DE;<code>valueOf</code>&#x65B9;&#x6CD5;&#x7684;&#x503C;&#xFF0C;&#x7B2C;&#x4E8C;&#x4E2A;&#x5BF9;&#x8C61;&#x8FD4;&#x56DE;<code>toString</code>&#x65B9;&#x6CD5;&#x7684;&#x503C;&#xFF0C;&#x7B2C;&#x4E09;&#x4E2A;&#x5BF9;&#x8C61;&#x8868;&#x793A;<code>valueOf</code>&#x65B9;&#x6CD5;&#x5148;&#x4E8E;<code>toString</code>&#x65B9;&#x6CD5;&#x6267;&#x884C;&#x3002;</p>
<h3 id="string">String()</h3>
<p><code>String</code>&#x51FD;&#x6570;&#x53EF;&#x4EE5;&#x5C06;&#x4EFB;&#x610F;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x8F6C;&#x5316;&#x6210;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x8F6C;&#x6362;&#x89C4;&#x5219;&#x5982;&#x4E0B;&#x3002;</p>
<p><strong>&#xFF08;1&#xFF09;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x503C;</strong></p>
<ul>
<li><strong>&#x6570;&#x503C;</strong>&#xFF1A;&#x8F6C;&#x4E3A;&#x76F8;&#x5E94;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x3002;</li>
<li><strong>&#x5B57;&#x7B26;&#x4E32;</strong>&#xFF1A;&#x8F6C;&#x6362;&#x540E;&#x8FD8;&#x662F;&#x539F;&#x6765;&#x7684;&#x503C;&#x3002;</li>
<li><strong>&#x5E03;&#x5C14;&#x503C;</strong>&#xFF1A;<code>true</code>&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;<code>&quot;true&quot;</code>&#xFF0C;<code>false</code>&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;<code>&quot;false&quot;</code>&#x3002;</li>
<li><strong>undefined</strong>&#xFF1A;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;<code>&quot;undefined&quot;</code>&#x3002;</li>
<li><strong>null</strong>&#xFF1A;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;<code>&quot;null&quot;</code>&#x3002;</li>
</ul>
<pre><code class="lang-javascript"><span class="hljs-built_in">String</span>(<span class="hljs-number">123</span>) <span class="hljs-comment">// &quot;123&quot;</span>
<span class="hljs-built_in">String</span>(<span class="hljs-string">&apos;abc&apos;</span>) <span class="hljs-comment">// &quot;abc&quot;</span>
<span class="hljs-built_in">String</span>(<span class="hljs-literal">true</span>) <span class="hljs-comment">// &quot;true&quot;</span>
<span class="hljs-built_in">String</span>(<span class="hljs-literal">undefined</span>) <span class="hljs-comment">// &quot;undefined&quot;</span>
<span class="hljs-built_in">String</span>(<span class="hljs-literal">null</span>) <span class="hljs-comment">// &quot;null&quot;</span>
</code></pre>
<p><strong>&#xFF08;2&#xFF09;&#x5BF9;&#x8C61;</strong></p>
<p><code>String</code>&#x65B9;&#x6CD5;&#x7684;&#x53C2;&#x6570;&#x5982;&#x679C;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x7C7B;&#x578B;&#x5B57;&#x7B26;&#x4E32;&#xFF1B;&#x5982;&#x679C;&#x662F;&#x6570;&#x7EC4;&#xFF0C;&#x8FD4;&#x56DE;&#x8BE5;&#x6570;&#x7EC4;&#x7684;&#x5B57;&#x7B26;&#x4E32;&#x5F62;&#x5F0F;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">String</span>({a: <span class="hljs-number">1</span>}) <span class="hljs-comment">// &quot;[object Object]&quot;</span>
<span class="hljs-built_in">String</span>([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]) <span class="hljs-comment">// &quot;1,2,3&quot;</span>
</code></pre>
<p><code>String</code>&#x65B9;&#x6CD5;&#x80CC;&#x540E;&#x7684;&#x8F6C;&#x6362;&#x89C4;&#x5219;&#xFF0C;&#x4E0E;<code>Number</code>&#x65B9;&#x6CD5;&#x57FA;&#x672C;&#x76F8;&#x540C;&#xFF0C;&#x53EA;&#x662F;&#x4E92;&#x6362;&#x4E86;<code>valueOf</code>&#x65B9;&#x6CD5;&#x548C;<code>toString</code>&#x65B9;&#x6CD5;&#x7684;&#x6267;&#x884C;&#x987A;&#x5E8F;&#x3002;</p>
<ol>
<li><p>&#x5148;&#x8C03;&#x7528;&#x5BF9;&#x8C61;&#x81EA;&#x8EAB;&#x7684;<code>toString</code>&#x65B9;&#x6CD5;&#x3002;&#x5982;&#x679C;&#x8FD4;&#x56DE;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5219;&#x5BF9;&#x8BE5;&#x503C;&#x4F7F;&#x7528;<code>String</code>&#x51FD;&#x6570;&#xFF0C;&#x4E0D;&#x518D;&#x8FDB;&#x884C;&#x4EE5;&#x4E0B;&#x6B65;&#x9AA4;&#x3002;</p>
</li>
<li><p>&#x5982;&#x679C;<code>toString</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x518D;&#x8C03;&#x7528;&#x539F;&#x5BF9;&#x8C61;&#x7684;<code>valueOf</code>&#x65B9;&#x6CD5;&#x3002;&#x5982;&#x679C;<code>valueOf</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5219;&#x5BF9;&#x8BE5;&#x503C;&#x4F7F;&#x7528;<code>String</code>&#x51FD;&#x6570;&#xFF0C;&#x4E0D;&#x518D;&#x8FDB;&#x884C;&#x4EE5;&#x4E0B;&#x6B65;&#x9AA4;&#x3002;</p>
</li>
<li><p>&#x5982;&#x679C;<code>valueOf</code>&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x5C31;&#x62A5;&#x9519;&#x3002;</p>
</li>
</ol>
<p>&#x4E0B;&#x9762;&#x662F;&#x4E00;&#x4E2A;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">String</span>({a: <span class="hljs-number">1</span>})
<span class="hljs-comment">// &quot;[object Object]&quot;</span>

<span class="hljs-comment">// &#x7B49;&#x540C;&#x4E8E;</span>
<span class="hljs-built_in">String</span>({a: <span class="hljs-number">1</span>}.toString())
<span class="hljs-comment">// &quot;[object Object]&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5148;&#x8C03;&#x7528;&#x5BF9;&#x8C61;&#x7684;<code>toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x53D1;&#x73B0;&#x8FD4;&#x56DE;&#x7684;&#x662F;&#x5B57;&#x7B26;&#x4E32;<code>[object Object]</code>&#xFF0C;&#x5C31;&#x4E0D;&#x518D;&#x8C03;&#x7528;<code>valueOf</code>&#x65B9;&#x6CD5;&#x4E86;&#x3002;</p>
<p>&#x5982;&#x679C;<code>toString</code>&#x6CD5;&#x548C;<code>valueOf</code>&#x65B9;&#x6CD5;&#xFF0C;&#x8FD4;&#x56DE;&#x7684;&#x90FD;&#x662F;&#x5BF9;&#x8C61;&#xFF0C;&#x5C31;&#x4F1A;&#x62A5;&#x9519;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> obj = {
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> {};
  },
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> {};
  }
};

<span class="hljs-built_in">String</span>(obj)
<span class="hljs-comment">// TypeError: Cannot convert object to primitive value</span>
</code></pre>
<p>&#x4E0B;&#x9762;&#x662F;&#x901A;&#x8FC7;&#x81EA;&#x5B9A;&#x4E49;<code>toString</code>&#x65B9;&#x6CD5;&#xFF0C;&#x6539;&#x53D8;&#x8FD4;&#x56DE;&#x503C;&#x7684;&#x4F8B;&#x5B50;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">String</span>({
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">3</span>;
  }
})
<span class="hljs-comment">// &quot;3&quot;</span>

<span class="hljs-built_in">String</span>({
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">2</span>;
  }
})
<span class="hljs-comment">// &quot;[object Object]&quot;</span>

<span class="hljs-built_in">String</span>({
  valueOf: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">2</span>;
  },
  toString: <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) </span>{
    <span class="hljs-keyword">return</span> <span class="hljs-number">3</span>;
  }
})
<span class="hljs-comment">// &quot;3&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x5BF9;&#x4E09;&#x4E2A;&#x5BF9;&#x8C61;&#x4F7F;&#x7528;<code>String</code>&#x51FD;&#x6570;&#x3002;&#x7B2C;&#x4E00;&#x4E2A;&#x5BF9;&#x8C61;&#x8FD4;&#x56DE;<code>toString</code>&#x65B9;&#x6CD5;&#x7684;&#x503C;&#xFF08;&#x6570;&#x503C;3&#xFF09;&#xFF0C;&#x7B2C;&#x4E8C;&#x4E2A;&#x5BF9;&#x8C61;&#x8FD4;&#x56DE;&#x7684;&#x8FD8;&#x662F;<code>toString</code>&#x65B9;&#x6CD5;&#x7684;&#x503C;&#xFF08;<code>[object Object]</code>&#xFF09;&#xFF0C;&#x7B2C;&#x4E09;&#x4E2A;&#x5BF9;&#x8C61;&#x8868;&#x793A;<code>toString</code>&#x65B9;&#x6CD5;&#x5148;&#x4E8E;<code>valueOf</code>&#x65B9;&#x6CD5;&#x6267;&#x884C;&#x3002;</p>
<h3 id="boolean">Boolean()</h3>
<p><code>Boolean()</code>&#x51FD;&#x6570;&#x53EF;&#x4EE5;&#x5C06;&#x4EFB;&#x610F;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x8F6C;&#x4E3A;&#x5E03;&#x5C14;&#x503C;&#x3002;</p>
<p>&#x5B83;&#x7684;&#x8F6C;&#x6362;&#x89C4;&#x5219;&#x76F8;&#x5BF9;&#x7B80;&#x5355;&#xFF1A;&#x9664;&#x4E86;&#x4EE5;&#x4E0B;&#x4E94;&#x4E2A;&#x503C;&#x7684;&#x8F6C;&#x6362;&#x7ED3;&#x679C;&#x4E3A;<code>false</code>&#xFF0C;&#x5176;&#x4ED6;&#x7684;&#x503C;&#x5168;&#x90E8;&#x4E3A;<code>true</code>&#x3002;</p>
<ul>
<li><code>undefined</code></li>
<li><code>null</code></li>
<li><code>0</code>&#xFF08;&#x5305;&#x542B;<code>-0</code>&#x548C;<code>+0</code>&#xFF09;</li>
<li><code>NaN</code></li>
<li><code>&apos;&apos;</code>&#xFF08;&#x7A7A;&#x5B57;&#x7B26;&#x4E32;&#xFF09;</li>
</ul>
<pre><code class="lang-javascript"><span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">undefined</span>) <span class="hljs-comment">// false</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">null</span>) <span class="hljs-comment">// false</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-number">0</span>) <span class="hljs-comment">// false</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">NaN</span>) <span class="hljs-comment">// false</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-string">&apos;&apos;</span>) <span class="hljs-comment">// false</span>
</code></pre>
<p>&#x5F53;&#x7136;&#xFF0C;<code>true</code>&#x548C;<code>false</code>&#x8FD9;&#x4E24;&#x4E2A;&#x5E03;&#x5C14;&#x503C;&#x4E0D;&#x4F1A;&#x53D1;&#x751F;&#x53D8;&#x5316;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">true</span>) <span class="hljs-comment">// true</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">false</span>) <span class="hljs-comment">// false</span>
</code></pre>
<p>&#x6CE8;&#x610F;&#xFF0C;&#x6240;&#x6709;&#x5BF9;&#x8C61;&#xFF08;&#x5305;&#x62EC;&#x7A7A;&#x5BF9;&#x8C61;&#xFF09;&#x7684;&#x8F6C;&#x6362;&#x7ED3;&#x679C;&#x90FD;&#x662F;<code>true</code>&#xFF0C;&#x751A;&#x81F3;&#x8FDE;<code>false</code>&#x5BF9;&#x5E94;&#x7684;&#x5E03;&#x5C14;&#x5BF9;&#x8C61;<code>new Boolean(false)</code>&#x4E5F;&#x662F;<code>true</code>&#xFF08;&#x8BE6;&#x89C1;&#x300A;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x503C;&#x7684;&#x5305;&#x88C5;&#x5BF9;&#x8C61;&#x300B;&#x4E00;&#x7AE0;&#xFF09;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-built_in">Boolean</span>({}) <span class="hljs-comment">// true</span>
<span class="hljs-built_in">Boolean</span>([]) <span class="hljs-comment">// true</span>
<span class="hljs-built_in">Boolean</span>(<span class="hljs-keyword">new</span> <span class="hljs-built_in">Boolean</span>(<span class="hljs-literal">false</span>)) <span class="hljs-comment">// true</span>
</code></pre>
<p>&#x6240;&#x6709;&#x5BF9;&#x8C61;&#x7684;&#x5E03;&#x5C14;&#x503C;&#x90FD;&#x662F;<code>true</code>&#xFF0C;&#x8FD9;&#x662F;&#x56E0;&#x4E3A; JavaScript &#x8BED;&#x8A00;&#x8BBE;&#x8BA1;&#x7684;&#x65F6;&#x5019;&#xFF0C;&#x51FA;&#x4E8E;&#x6027;&#x80FD;&#x7684;&#x8003;&#x8651;&#xFF0C;&#x5982;&#x679C;&#x5BF9;&#x8C61;&#x9700;&#x8981;&#x8BA1;&#x7B97;&#x624D;&#x80FD;&#x5F97;&#x5230;&#x5E03;&#x5C14;&#x503C;&#xFF0C;&#x5BF9;&#x4E8E;<code>obj1 &amp;&amp; obj2</code>&#x8FD9;&#x6837;&#x7684;&#x573A;&#x666F;&#xFF0C;&#x53EF;&#x80FD;&#x4F1A;&#x9700;&#x8981;&#x8F83;&#x591A;&#x7684;&#x8BA1;&#x7B97;&#x3002;&#x4E3A;&#x4E86;&#x4FDD;&#x8BC1;&#x6027;&#x80FD;&#xFF0C;&#x5C31;&#x7EDF;&#x4E00;&#x89C4;&#x5B9A;&#xFF0C;&#x5BF9;&#x8C61;&#x7684;&#x5E03;&#x5C14;&#x503C;&#x4E3A;<code>true</code>&#x3002;</p>
<h2 id="&#x81EA;&#x52A8;&#x8F6C;&#x6362;">&#x81EA;&#x52A8;&#x8F6C;&#x6362;</h2>
<p>&#x4E0B;&#x9762;&#x4ECB;&#x7ECD;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#xFF0C;&#x5B83;&#x662F;&#x4EE5;&#x5F3A;&#x5236;&#x8F6C;&#x6362;&#x4E3A;&#x57FA;&#x7840;&#x7684;&#x3002;</p>
<p>&#x9047;&#x5230;&#x4EE5;&#x4E0B;&#x4E09;&#x79CD;&#x60C5;&#x51B5;&#x65F6;&#xFF0C;JavaScript &#x4F1A;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x6570;&#x636E;&#x7C7B;&#x578B;&#xFF0C;&#x5373;&#x8F6C;&#x6362;&#x662F;&#x81EA;&#x52A8;&#x5B8C;&#x6210;&#x7684;&#xFF0C;&#x7528;&#x6237;&#x4E0D;&#x53EF;&#x89C1;&#x3002;</p>
<p>&#x7B2C;&#x4E00;&#x79CD;&#x60C5;&#x51B5;&#xFF0C;&#x4E0D;&#x540C;&#x7C7B;&#x578B;&#x7684;&#x6570;&#x636E;&#x4E92;&#x76F8;&#x8FD0;&#x7B97;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-number">123</span> + <span class="hljs-string">&apos;abc&apos;</span> <span class="hljs-comment">// &quot;123abc&quot;</span>
</code></pre>
<p>&#x7B2C;&#x4E8C;&#x79CD;&#x60C5;&#x51B5;&#xFF0C;&#x5BF9;&#x975E;&#x5E03;&#x5C14;&#x503C;&#x7C7B;&#x578B;&#x7684;&#x6570;&#x636E;&#x6C42;&#x5E03;&#x5C14;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">if</span> (<span class="hljs-string">&apos;abc&apos;</span>) {
  <span class="hljs-built_in">console</span>.log(<span class="hljs-string">&apos;hello&apos;</span>)
}  <span class="hljs-comment">// &quot;hello&quot;</span>
</code></pre>
<p>&#x7B2C;&#x4E09;&#x79CD;&#x60C5;&#x51B5;&#xFF0C;&#x5BF9;&#x975E;&#x6570;&#x503C;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x4F7F;&#x7528;&#x4E00;&#x5143;&#x8FD0;&#x7B97;&#x7B26;&#xFF08;&#x5373;<code>+</code>&#x548C;<code>-</code>&#xFF09;&#x3002;</p>
<pre><code class="lang-javascript">+ {foo: <span class="hljs-string">&apos;bar&apos;</span>} <span class="hljs-comment">// NaN</span>
- [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>] <span class="hljs-comment">// NaN</span>
</code></pre>
<p>&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x7684;&#x89C4;&#x5219;&#x662F;&#x8FD9;&#x6837;&#x7684;&#xFF1A;&#x9884;&#x671F;&#x4EC0;&#x4E48;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x5C31;&#x8C03;&#x7528;&#x8BE5;&#x7C7B;&#x578B;&#x7684;&#x8F6C;&#x6362;&#x51FD;&#x6570;&#x3002;&#x6BD4;&#x5982;&#xFF0C;&#x67D0;&#x4E2A;&#x4F4D;&#x7F6E;&#x9884;&#x671F;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x5C31;&#x8C03;&#x7528;<code>String</code>&#x51FD;&#x6570;&#x8FDB;&#x884C;&#x8F6C;&#x6362;&#x3002;&#x5982;&#x679C;&#x8BE5;&#x4F4D;&#x7F6E;&#x5373;&#x53EF;&#x4EE5;&#x662F;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x4E5F;&#x53EF;&#x80FD;&#x662F;&#x6570;&#x503C;&#xFF0C;&#x90A3;&#x4E48;&#x9ED8;&#x8BA4;&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#x3002;</p>
<p>&#x7531;&#x4E8E;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x5177;&#x6709;&#x4E0D;&#x786E;&#x5B9A;&#x6027;&#xFF0C;&#x800C;&#x4E14;&#x4E0D;&#x6613;&#x9664;&#x9519;&#xFF0C;&#x5EFA;&#x8BAE;&#x5728;&#x9884;&#x671F;&#x4E3A;&#x5E03;&#x5C14;&#x503C;&#x3001;&#x6570;&#x503C;&#x3001;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x5730;&#x65B9;&#xFF0C;&#x5168;&#x90E8;&#x4F7F;&#x7528;<code>Boolean</code>&#x3001;<code>Number</code>&#x548C;<code>String</code>&#x51FD;&#x6570;&#x8FDB;&#x884C;&#x663E;&#x5F0F;&#x8F6C;&#x6362;&#x3002;</p>
<h3 id="&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x5E03;&#x5C14;&#x503C;">&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x5E03;&#x5C14;&#x503C;</h3>
<p>JavaScript &#x9047;&#x5230;&#x9884;&#x671F;&#x4E3A;&#x5E03;&#x5C14;&#x503C;&#x7684;&#x5730;&#x65B9;&#xFF08;&#x6BD4;&#x5982;<code>if</code>&#x8BED;&#x53E5;&#x7684;&#x6761;&#x4EF6;&#x90E8;&#x5206;&#xFF09;&#xFF0C;&#x5C31;&#x4F1A;&#x5C06;&#x975E;&#x5E03;&#x5C14;&#x503C;&#x7684;&#x53C2;&#x6570;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x5E03;&#x5C14;&#x503C;&#x3002;&#x7CFB;&#x7EDF;&#x5185;&#x90E8;&#x4F1A;&#x81EA;&#x52A8;&#x8C03;&#x7528;<code>Boolean</code>&#x51FD;&#x6570;&#x3002;</p>
<p>&#x56E0;&#x6B64;&#x9664;&#x4E86;&#x4EE5;&#x4E0B;&#x4E94;&#x4E2A;&#x503C;&#xFF0C;&#x5176;&#x4ED6;&#x90FD;&#x662F;&#x81EA;&#x52A8;&#x8F6C;&#x4E3A;<code>true</code>&#x3002;</p>
<ul>
<li><code>undefined</code></li>
<li><code>null</code></li>
<li><code>+0</code>&#x6216;<code>-0</code></li>
<li><code>NaN</code></li>
<li><code>&apos;&apos;</code>&#xFF08;&#x7A7A;&#x5B57;&#x7B26;&#x4E32;&#xFF09;</li>
</ul>
<p>&#x4E0B;&#x9762;&#x8FD9;&#x4E2A;&#x4F8B;&#x5B50;&#x4E2D;&#xFF0C;&#x6761;&#x4EF6;&#x90E8;&#x5206;&#x7684;&#x6BCF;&#x4E2A;&#x503C;&#x90FD;&#x76F8;&#x5F53;&#x4E8E;<code>false</code>&#xFF0C;&#x4F7F;&#x7528;&#x5426;&#x5B9A;&#x8FD0;&#x7B97;&#x7B26;&#x540E;&#xFF0C;&#x5C31;&#x53D8;&#x6210;&#x4E86;<code>true</code>&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">if</span> ( !<span class="hljs-literal">undefined</span>
  &amp;&amp; !<span class="hljs-literal">null</span>
  &amp;&amp; !<span class="hljs-number">0</span>
  &amp;&amp; !<span class="hljs-literal">NaN</span>
  &amp;&amp; !<span class="hljs-string">&apos;&apos;</span>
) {
  <span class="hljs-built_in">console</span>.log(<span class="hljs-string">&apos;true&apos;</span>);
} <span class="hljs-comment">// true</span>
</code></pre>
<p>&#x4E0B;&#x9762;&#x4E24;&#x79CD;&#x5199;&#x6CD5;&#xFF0C;&#x6709;&#x65F6;&#x4E5F;&#x7528;&#x4E8E;&#x5C06;&#x4E00;&#x4E2A;&#x8868;&#x8FBE;&#x5F0F;&#x8F6C;&#x4E3A;&#x5E03;&#x5C14;&#x503C;&#x3002;&#x5B83;&#x4EEC;&#x5185;&#x90E8;&#x8C03;&#x7528;&#x7684;&#x4E5F;&#x662F;<code>Boolean</code>&#x51FD;&#x6570;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-comment">// &#x5199;&#x6CD5;&#x4E00;</span>
expression ? <span class="hljs-literal">true</span> : <span class="hljs-literal">false</span>

<span class="hljs-comment">// &#x5199;&#x6CD5;&#x4E8C;</span>
!! expression
</code></pre>
<h3 id="&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;">&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;</h3>
<p>JavaScript &#x9047;&#x5230;&#x9884;&#x671F;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x5730;&#x65B9;&#xFF0C;&#x5C31;&#x4F1A;&#x5C06;&#x975E;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x503C;&#x81EA;&#x52A8;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#x3002;&#x5177;&#x4F53;&#x89C4;&#x5219;&#x662F;&#xFF0C;&#x5148;&#x5C06;&#x590D;&#x5408;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x8F6C;&#x4E3A;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#xFF0C;&#x518D;&#x5C06;&#x539F;&#x59CB;&#x7C7B;&#x578B;&#x7684;&#x503C;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#x3002;</p>
<p>&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#xFF0C;&#x4E3B;&#x8981;&#x53D1;&#x751F;&#x5728;&#x5B57;&#x7B26;&#x4E32;&#x7684;&#x52A0;&#x6CD5;&#x8FD0;&#x7B97;&#x65F6;&#x3002;&#x5F53;&#x4E00;&#x4E2A;&#x503C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x53E6;&#x4E00;&#x4E2A;&#x503C;&#x4E3A;&#x975E;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x5219;&#x540E;&#x8005;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-number">1</span> <span class="hljs-comment">// &apos;51&apos;</span>
<span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-literal">true</span> <span class="hljs-comment">// &quot;5true&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-literal">false</span> <span class="hljs-comment">// &quot;5false&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + {} <span class="hljs-comment">// &quot;5[object Object]&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + [] <span class="hljs-comment">// &quot;5&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-function"><span class="hljs-keyword">function</span> (<span class="hljs-params"></span>)</span>{} <span class="hljs-comment">// &quot;5function (){}&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-literal">undefined</span> <span class="hljs-comment">// &quot;5undefined&quot;</span>
<span class="hljs-string">&apos;5&apos;</span> + <span class="hljs-literal">null</span> <span class="hljs-comment">// &quot;5null&quot;</span>
</code></pre>
<p>&#x8FD9;&#x79CD;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x5F88;&#x5BB9;&#x6613;&#x51FA;&#x9519;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-keyword">var</span> obj = {
  width: <span class="hljs-string">&apos;100&apos;</span>
};

obj.width + <span class="hljs-number">20</span> <span class="hljs-comment">// &quot;10020&quot;</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x5F00;&#x53D1;&#x8005;&#x53EF;&#x80FD;&#x671F;&#x671B;&#x8FD4;&#x56DE;<code>120</code>&#xFF0C;&#x4F46;&#x662F;&#x7531;&#x4E8E;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#xFF0C;&#x5B9E;&#x9645;&#x4E0A;&#x8FD4;&#x56DE;&#x4E86;&#x4E00;&#x4E2A;&#x5B57;&#x7B26;<code>10020</code>&#x3002;</p>
<h3 id="&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x6570;&#x503C;">&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x6570;&#x503C;</h3>
<p>JavaScript &#x9047;&#x5230;&#x9884;&#x671F;&#x4E3A;&#x6570;&#x503C;&#x7684;&#x5730;&#x65B9;&#xFF0C;&#x5C31;&#x4F1A;&#x5C06;&#x53C2;&#x6570;&#x503C;&#x81EA;&#x52A8;&#x8F6C;&#x6362;&#x4E3A;&#x6570;&#x503C;&#x3002;&#x7CFB;&#x7EDF;&#x5185;&#x90E8;&#x4F1A;&#x81EA;&#x52A8;&#x8C03;&#x7528;<code>Number</code>&#x51FD;&#x6570;&#x3002;</p>
<p>&#x9664;&#x4E86;&#x52A0;&#x6CD5;&#x8FD0;&#x7B97;&#x7B26;&#xFF08;<code>+</code>&#xFF09;&#x6709;&#x53EF;&#x80FD;&#x628A;&#x8FD0;&#x7B97;&#x5B50;&#x8F6C;&#x4E3A;&#x5B57;&#x7B26;&#x4E32;&#xFF0C;&#x5176;&#x4ED6;&#x8FD0;&#x7B97;&#x7B26;&#x90FD;&#x4F1A;&#x628A;&#x8FD0;&#x7B97;&#x5B50;&#x81EA;&#x52A8;&#x8F6C;&#x6210;&#x6570;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript"><span class="hljs-string">&apos;5&apos;</span> - <span class="hljs-string">&apos;2&apos;</span> <span class="hljs-comment">// 3</span>
<span class="hljs-string">&apos;5&apos;</span> * <span class="hljs-string">&apos;2&apos;</span> <span class="hljs-comment">// 10</span>
<span class="hljs-literal">true</span> - <span class="hljs-number">1</span>  <span class="hljs-comment">// 0</span>
<span class="hljs-literal">false</span> - <span class="hljs-number">1</span> <span class="hljs-comment">// -1</span>
<span class="hljs-string">&apos;1&apos;</span> - <span class="hljs-number">1</span>   <span class="hljs-comment">// 0</span>
<span class="hljs-string">&apos;5&apos;</span> * []    <span class="hljs-comment">// 0</span>
<span class="hljs-literal">false</span> / <span class="hljs-string">&apos;5&apos;</span> <span class="hljs-comment">// 0</span>
<span class="hljs-string">&apos;abc&apos;</span> - <span class="hljs-number">1</span>   <span class="hljs-comment">// NaN</span>
<span class="hljs-literal">null</span> + <span class="hljs-number">1</span> <span class="hljs-comment">// 1</span>
<span class="hljs-literal">undefined</span> + <span class="hljs-number">1</span> <span class="hljs-comment">// NaN</span>
</code></pre>
<p>&#x4E0A;&#x9762;&#x4EE3;&#x7801;&#x4E2D;&#xFF0C;&#x8FD0;&#x7B97;&#x7B26;&#x4E24;&#x4FA7;&#x7684;&#x8FD0;&#x7B97;&#x5B50;&#xFF0C;&#x90FD;&#x88AB;&#x8F6C;&#x6210;&#x4E86;&#x6570;&#x503C;&#x3002;</p>
<blockquote>
<p>&#x6CE8;&#x610F;&#xFF1A;<code>null</code>&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#x65F6;&#x4E3A;<code>0</code>&#xFF0C;&#x800C;<code>undefined</code>&#x8F6C;&#x4E3A;&#x6570;&#x503C;&#x65F6;&#x4E3A;<code>NaN</code>&#x3002;</p>
</blockquote>
<p>&#x4E00;&#x5143;&#x8FD0;&#x7B97;&#x7B26;&#x4E5F;&#x4F1A;&#x628A;&#x8FD0;&#x7B97;&#x5B50;&#x8F6C;&#x6210;&#x6570;&#x503C;&#x3002;</p>
<pre><code class="lang-javascript">+<span class="hljs-string">&apos;abc&apos;</span> <span class="hljs-comment">// NaN</span>
-<span class="hljs-string">&apos;abc&apos;</span> <span class="hljs-comment">// NaN</span>
+<span class="hljs-literal">true</span> <span class="hljs-comment">// 1</span>
-<span class="hljs-literal">false</span> <span class="hljs-comment">// 0</span>
</code></pre>
<h2 id="&#x53C2;&#x8003;&#x94FE;&#x63A5;">&#x53C2;&#x8003;&#x94FE;&#x63A5;</h2>
<ul>
<li>Axel Rauschmayer, <a href="http://www.2ality.com/2012/01/object-plus-object.html" target="_blank" rel="nofollow">What is {} + {} in JavaScript?</a></li>
<li>Axel Rauschmayer, <a href="http://www.2ality.com/2013/04/quirk-implicit-conversion.html" target="_blank" rel="nofollow">JavaScript quirk 1: implicit conversion of values</a></li>
<li>Benjie Gillam, <a href="http://www.benjiegillam.com/2013/06/quantum-javascript/" target="_blank" rel="nofollow">Quantum JavaScript?</a></li>
</ul>




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